It has been known for some time to dispense materials stored in a container by moving a piston longitudinally through the container toward a product outlet. Movement of the piston is effected by a longitudinal strap (i.e., either a strand bendable in three dimensions or a ribbon bendable in two dimensions) having one end connected to the piston and the other end attached to an actuating lever externally accessible with respect to the container. However, prior art strap dispensers have had a significant problem with leakage of flowable materials proximate to where the strap passes from within the container to its exterior. As a result, it has been necessary to withdraw the strap from within the container at a location behind the piston where no material to be dispensed is present, as shown in U.S. Pat. No. 3,229,865 to Heisler et al. ("Heisler"), U.S. Pat. No. 1,025,511 to Craven ("Craven"), and U.S. Pat. No. 1,810,249 to Koehler ("Koehler"). In Heisler and Koehler, the piston or product conveying element is pushed toward the dispenser outlet using a rigid strap. This type of strap, as opposed to one which pulls the piston, adds significantly to the weight of the dispense. When, however, the strap pulls the piston, it is necessary to prevent leakage by providing a hole in the piston through which the strap exits, as shown by Craven. At this location distal from the product outlet, leakage is unlikely, but a more complicated structural arrangement is required. Only when a non-flowable material is dispensed has it been possible to withdraw the strap from the container interior above the piston, as taught by U.S. Pat. No. 3,231,139 to Bouet.